1. Technical Field
The field relates to modulation of water flow for the generation of sound.
2. Description of the Problem
Underwater Sound Sources Designed Around Helmholtz-Resonator Like configurations are known. Since water is substantially incompressible, the compliance function of a Helmholtz resonance chamber is implemented by adaptation of the resonance chamber into a “compliance chamber.” This has been done by providing “compliance tubes” in the chambers among other techniques. Unlike what occurs where a compressible fluid/gas fills a resonance chamber, it is not chamber size which determines chamber compliance due to compressibility of the gas, but rather the compressibility of the compliance tubes. See Woollett, Ralph S.; Underwater Helmholtz-Resonator Transducers: General Design Principles; Naval Underwater Systems Center; NUSC Technical Report 5633 (5 Jul. 1977). Such systems have been designed using ceramic piezoelectric transducers as an excitation source to radiate sound at frequencies below 100 Hz even while the transducer operates at a much higher frequency. These devices function to provide a strong output peak at a Helmholtz like resonance, however, the greatest energy input is at the resonant frequency of the transducer.
Another technique for producing sound in liquids, in this case ultrasonic sound, has been the so-called underwater whistle. An example of such a system is described in Gaffney, U.S. Pat. No. 4,675,194. The '194 patent describes a device in which streams of liquids are directed through an orifice into a resonance chamber to impinge against a “vibratile element.” Energy is transferred from the stream to the vibratile element which results in the vibratile element vibrating at ultrasonic frequencies. The vibratile element is constructed in the form of a blade which is positioned oriented parallel to and aimed into the directed streams of liquid. The sound generated by the blade promotes reactions between materials carried in the streams. A positive displacement pump is generally used to place the liquid under pressure for discharge. The jets of liquid from the orifice also shed vortices perpendicular to the direction of liquid flow and generate cavitation effects. Most underwater whistles appear to have been applied to promoting mixing of different materials through ultrasonic agitation.